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== Study Questions ==
* <spoiler text="Does everyone with a positive PPD test have TB?">No, it just indicates exposure to a ''Mycobacterium'' species, many of which are non-pathogenic in humans. Those who have received Bacillus Calmette–Guérin (BCG) vaccination, for instance, routinely have a positive PPD test even though they have never been exposed to ''Mycobacterium tuberculosis''.</spoiler>
* <spoiler text="How does this lesion differ from the lesions seen in sarcoid?">These are caseating granulomas with a central region of caseation necrosis and macrophages and lymphocytes around the periphery. Multinucleated, primarily Langhans’ type, giant cells are present within these nodules.</spoiler>
* <spoiler text="What are epithelioid cells?">Epitheliod cells are tissue macrophages that have an epithelium-like appearance.</spoiler>